A key transcriptional factor, the signal transducer and activator of transcription (STAT) 3, drives the tumorigenic components of malignant gliomas and is commonly over expressed. Phosphorylated STATS propagates tumorigenesis, including the glioma cancer stem cell (GSC) contribution, by enhancing proliferation, angiogenesis, invasion, and immunosuppression. We have developed WP1066, a potent orally administered inhibitor of STAT3 with excellent blood-brain-barrier penetration that displays marked efficacy against established intracerebral heterogeneous gliomas in vivo. We have demonstrated that a significant mechanism of WP1066's activity is a combination of both direct anti-tumor effects and the reversal of tumor-mediated immune suppression. In this proposed study, we hypothesize that that in addition to directly inhibiting cell proliferation, angiogenesis, and stemness, targeting p-STATS with the small molecule inhibitor WP1066 results in a therapeutically significant reversal of GBM-mediated immune suppression leading to improved patient survival. To test our hypothesis, our first aim will explore whether the immunological status of the tumor might influence the response to STAT3 blockade. This will involve correlating immune responses to GBM subtypes using The Cancer Genome Atlas and then validating these findings with immunohistochemistry and immune functional assays. This premise will be formally tested in murine models and then in human patients in Specific Aim 2. Given the importance of temozolomide in the treatment of GBM patients, we will then explore the therapeutic effects and immune modulation of the combination of WP1066 and temozolomide on the GSC and within murine models, which may influence, the selected targeted patient population during later clinical trials. Moreover, we will investigate a paradigm shifting concept of whether by simply controlling tumor-mediated immune suppression, sufficient anti-tumor immunity is induced for tumor clearance. Successful completion of this project could result in a novel agent that not only could impact the survival of malignant glioma patients but would also have therapeutic application for a wide variety of other malignancies, including those that metastasis to the brain. RELEVANCE: DO NOT EXCEED THE SPACE PROVIDED. The development of new, effective therapies for malignant gliomas that target novel pathways associated with central nervous system malignancies is a major unmet clinical need. This proposal will test a novel, small molecular inhibitor of the signal transduction and activator of transcription, (STAT)-3 pathway, key to tumorigenesis and immune suppression, for implementation in patients with established CNS malignancies.